This invention relates to a liquid dispensing and vapor recovery system and, more particularly, to such a system in which liquid is dispensed from a storage tank to a receptacle while vapors from the receptacle are drawn to the storage tank.
With the increased emphasis on preventing pollution of the atmosphere, recent attention has been directed to minimizing the introduction of gasoline vapors into the atmosphere from both permanent type underground storage tanks for the gasoline, and from the vehicles into which the gasoline is ultimately dispensed.
Gasoline vapors can easily be recovered from underground storage tanks by providing a separate vapor return line which connects the storage tank to the transport truck which periodically fills the tank. In this manner, the gasoline introduced into the tank from the transport truck will displace the vapors and force them through the vapor recovery line to the truck whereby they are ultimately disposed of either by burning or through compression-refrigeration systems.
One system that has been used for the purpose of recovering vapors from the gasoline tanks of vehicles is what is normally referred to as a balanced displacement system in which the gasoline entering the vehicle tank forces the vapors that accumulate in the latter tank through a separate line to the storage tank.
Another system that has recently evolved involves an injector, an aspirator, or the like which forms a reduced pressure zone in response to the gasoline flow from the storage tank, which reduced pressure zone is connected to the vehicle tank for drawing the vapor from the vehicle tank and returning same to the storage tank. An example of this type system is disclosed in U.S. Pat. Nos. 3,941,168, 3,952,781, 3,981,334 and 3,981,335.
In both of the foregoing systems, it is highly desirable that the vapor should pass from the vehicle tank to the storage tank in one of the aforementioned manners in response to a relatively very low pressure drop between the tanks. Also, the flow of vapor from the storage tank through the vapor line to the vehicle tank should be normally prevented but should be permitted in the event the pressure in the storage tank builds up to abnormally high levels, which may occur, for example, when gasoline is dispensed from a transport truck or the like into the storage tank.